Best practice in LUN design

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    The LUN design "question"

    How many LUN, how bigger (or smaller), on how many physical disks?

    You can find different post about this "problem"...

     

    There isn't a simple answer, cause it depends on:

    • Storage best practice

    • Storage type and disks type

    • RAID level and number of physical disks

    • VM number, size and type of I/O

    • Max VM and I/O per LUN

    • Max LUN size (less than 2 TB - 512B)

     

    Generally it's not a good idea to have very large LUNs: when you have a large number of VMs on a single VMFS based block device you will see a higher level of SCSI Reservation Conflicts which always results in performance degregation.

    This occurs because the clustered VMFS LUN uses a file lock control function from the hosts and the higher the VM count the more often they have to wait on each others update housekeeping I/O activity.

     

    See also:

    SAN Configuration Guide - http://www.vmware.com/pdf/vi3_esx_san_cfg.pdf

    SAN Conceptual and Design Basics - http://www.vmware.com/pdf/esx_san_cfg_technote.pdf

    SAN System Design and Deployment Guide - http://www.vmware.com/pdf/vi3_san_design_deploy.pdf

     

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    LUN size

    Usually a value between 400-800GB could be reasonable.

    There is also a way to calculate the size, see on this site:

    Storage: How to size your LUNs? - http://www.gabesvirtualworld.com/?p=68

     

    Here are some good threads that talk about this....

    http://searchvmware.techtarget.com/tip/0,289483,sid179_gci1350469,00.html

    http://malaysiavm.com/blog/best-sizing-for-single-storage-lun/

    LUN size

    Re: Disk files and LUN's

    Re: Sizing LUN for enough free space after VM

    San Sizing documentation request...

    Smaller LUNs or Bigger LUNs?

    Larger LUN = More Disks = More Performance

    Best Practice LUN Size

    Storage LUNs Size Sweet Spot

     

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    LUN number

    Usually more that one, but not too much...

    It is also related by LUN size and how storage works (it works with RAID group or with a "global" RAID splitted on all disks)

     

    Here are some good threads that talk about this....

    Re: which is better, more or fewer disks for VM local storage??

    Re: Should we have one Large VMFS-3 volume or small Multiple volumes?

    Re: which is better, more or fewer disks for VM local storage??

     

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    RAID level

    Re: How to configure the raid while installing the ESX Server

    ARTICLE: RAID 5/6 Scaling (Tom's HW)